Acoustic detection using optical fibers exploits Rayleigh back-scattering along a fiber from a short pulse of light traversing the fiber. The back-scattering characteristics change if the fiber is moved or deformed even on the micron-scale. Thus, a record of changes in scattering intensity as a function of pulse transit time correspond to movement of the fiber as a function of position along the fiber. This results in a distributed acoustic sensor that can be used for well diagnostics in the oil field on either a temporary or even permanent installed basis. Such fiber based sensors can be used to detect the acoustic signature of small leaks, flows, and bubbles within a wellbore or borehole.